The issue of disposability of products is of great concern to the nonwovens industry. Landfills, incineration, multiple sewage treatment and residential septic systems are among the common choices for nonwoven product disposal today. Products targeted for the latter disposal routes, via residential and commercial toilets, are termed flushable. Current flushable products have limitations. Dry products, such as bathroom tissue, have been designed with minimal wet strength so that the tissue can disintegrate under the agitation in the plumbing systems. They are not designed for applications where water will be encountered in use. Flushable wet wipes have high wet strengths and do not lose their strength upon disposal. These products remain intact and identifiable in the disposal system.
Wet-packaged skin cleansing and refreshing tissues are well known commercially, generally referred to as towelettes, wet wipes, fem wipes and the like. These may comprise an absorbent sheet made of paper, prepared or treated to impart wet strength thereto, having the dimensions of the usual wash cloth and packaged wet in folded condition, individually in impervious envelopes or in multiples in closed containers. The liquid employed in the pre-moistening of the sheet is generally an aqueous alcoholic solution which may further contain a surface active detergent and a humectant and, in some instances, also a scenting agent. Instead of individual packaging of such moist sheets, they are often marketed in reclosable containers having any desired convenient number of such folded sheets.
U.S. Pat. No. 3,689,314 discloses a method for making a flushable wrapper by treating a nonwoven web with an aqueous solution containing polyvinyl alcohol, boric acid and sodium bicarbonate, heating the web to a temperature sufficient to cause the boric acid and sodium bicarbonate to react and form borax, and to continue to heat the web to dry it so that substantially all of the borax crosslinks with the polyvinyl alcohol. The boric acid and sodium bicarbonate are used in such amounts as to generate at least 2 wt% borax based on the polyvinyl alcohol.
U.S. Pat. Nos. 4,258,849 and 4,245,744 disclose pre-moistened towelettes which are flushable. These towelettes incorporate a polyvinyl alcohol (PVOH) or PVOH stabilized polymer emulsion as a binder, respectively, and an aqueous pre-moistening lotion which contains salts (especially boric acid) that insolubilize the PVOH to impart good strength and integrity. Relatively high salt concentrations are required to impart good strength. For example, useful performance is not achieved until at least 3% boric acid is used. While other useful insolubilizing salts for PVOH need to be used at much higher concentrations to achieve the same effect, wipes prepared with these types of binders rapidly disintegrate in water by reduction in salt concentration and solubilization of the PVOH based binder.
U.S. Pat. No. 4,309,469 discloses a three component adhesive for nonwoven webs in combination with a water based lotion containing borate ions. The components of the adhesive composition applied to the web are PVOH, a non-self-crosslinking, thermosetting, polymer emulsion and a self-crosslinking, thermosetting polymer emulsion. An organic acid capable of complexing with borate, such as .alpha.-hydroxy acids or o-aromatic hydroxy acids, is claimed to produce a synergistic effect upon the PVOH adhesive in the web.
Due to some ingestion toxicity concerns, pre-moistened towelette manufacturers would require the reduction of the aqueous boric acid or borax (sodium tetraborate) solution from the 3-5% concentration level to 1% or less while still achieving a useful tensile strength of at least about 1.3 pli (.about.230 glc) in order to have a commercially viable product.